Magnetic extracts of three gravity cores located at the Ceará Rise, the Mid-Atlantic Ridge and the Sierra Leone Rise

The magnetic microparticle and nanoparticle inventories of marine sediments from equatorial Atlantic sites were investigated by scanning and transmission electron microscopy to classify all present detrital and authigenic magnetic mineral species and to investigate their regional distribution, origin, transport, and preservation. This information is used to establish source-to-sink relations and to constrain environmental magnetic proxy interpretations for this area. Magnetic extracts were prepared from sediments of three supralysoclinal open ocean gravity cores located at the Ceará Rise (GeoB 1523-1; 3°49.9'N/41°37.3'W), the Mid-Atlantic Ridge (GeoB 4313-2; 4°02.8'N/33°26.3'W), and the Sierra Leone Rise (GeoB 2910-1; 4°50.7'N/21°03.2'W). Sediments from two depths corresponding to marine isotope stages 4 and 5.5 were processed. This selection represents glacial and interglacial conditions of sedimentation for the western, central, and eastern equatorial Atlantic and avoids interferences from subsurface and anoxic processes. Crystallographic, elemental, morphological, and granulometric data of more than 2000 magnetic particles were collected by scanning and transmission electron microscopy. On basis of these properties, nine particle classes could be defined: detrital magnetite, titanomagnetite (fragmental and euhedral), titanomagnetite-hemoilmentite intergrowths, silicates with magnetic inclusions, microcrystalline hematite, magnetite spherules, bacterial magnetite, goethite needles, and nanoparticle clusters. Each class can be associated with fluvial, eolian, subaeric, and submarine volcanic, biogenic, or chemogenic sources. Large-scale sedimentation patterns are delineated as well: detrital magnetite is typical of Amazon discharge, fragmental titanomagnetite is a submarine weathering product of mid-ocean ridge basalts, and titanomagnetite-hemoilmenite intergrowths are common magnetic particles in West African dust. This clear regionalization underlines that magnetic petrology is an excellent indicator of source-to-sink relations. Hematite encrustations, magnetic spherules, and nanoparticle clusters were found at all investigated sites, while bacterial magnetite and authigenic hematite were only detected at the more oxic western site. At the eastern site, surface pits and crevices were seen on the crystal faces indicating subtle early diagenetic reductive dissolution. It was observed that paleoclimatic signatures of magnetogranulometric parameters such as the ratio of anhysteretic and isothermal remanent magnetizations can be formed either by mixing of multiple sources with separate, relatively narrow grain size ranges (western site) or by variable sorting of a single source with a broad grain size distribution (eastern site). Hematite, goethite, and possibly ferrihydrite nanoparticles occur in all sediment cores studied and have either high-coercive or superparamagnetic properties depending on their partly ultrafine grain sizes. These two magnetic fractions are generally discussed as separate fractions, but we suggest that they could actually be genetically linked.

Continuous measurement of carbon dioxid partial pressure in seawater in the region of the Iceland-Faroe Ridge (Table 1)

During the 14th expedition of the research vessel "Meteor" from the 2nd of July to the 7th of August 1968 continously recording instruments for measuring the CO2 partial pressure of seawater and atmospheric CO2 were developped by the Meteorological Institute, University of Frankfurt/M. During the Faroer expedition instrumental constants, such as relative and absolute accuracy, inertia and solvent power were tested. The performance of discontinous analyses of water samples was adopted to shipboard conditiones and correction factors depending on water volume, depth of sampling and water temperature were measured. After having computed average values of the continous records (atmosp. CO2 content, CO2 partial pressure, water temperature) geographical distribution, diurnal variation and dependence of diurnal averages were tested. At four different locations CO2 partial pressure was measured in various depths. During the voyage from the Faroer islands to Helgoland the measured concentrations of atmospheric CO2 content and CO2 partial pressure were tested with respect to a correlation of the geographical latitude.

Calcite saturation and dissolution index of core-top sediment samples from the Ontong Java Plateau, Mid-Atlantic Ridge, the Caribbean and the Ceara Rise, the Indian Ocean, the Ninety-East Ridge and from the east of Madagascar

X-ray computed tomography (CT) provides an insight into the progression of dissolution in the tests of planktonic foraminifera. Four species of foraminifera (G. ruber [white], G. sacculifer, N. dutertrei and P. obliquiloculata) from Pacific, Atlantic and Indian Ocean core-top samples were examined by CT and SEM. Inner chamber walls began to dissolve at Delta[CO3**2-] values of 12-14 µmol/kg. Close to the calcite saturation horizon, dissolution and precipitation of calcite may occur simultaneously. Inner calcite of G. sacculifer, N. dutertrei and P. obliquiloculata from such sites appeared altered or replaced, whereas outer crust calcite was dense with no pores. Unlike the other species, there was no distinction between inner and outer calcite in CT scans of G. ruber. Empty calcite crusts of N. dutertrei and P. obliquiloculata were most resistant to dissolution and were present in samples where Delta[CO3**2-] ~ -20 µmol/kg. Five stages of preservation were identified in CT scans, and an empirical dissolution index, XDX, was established. XDX appears to be insensitive to initial test mass. Mass loss in response to dissolution was similar between species and sites at ~ 0.4 µg/µmol/kg. We provide calibrations to estimate Delta[CO3**2-] and initial test mass from XDX.

(Supplement Table1) Abundances of major elements from KH93-3_DR10 at the Southwest Indian Ridge near the Rodriguez Triple Junction

Petrographic and geochemical analyses of basaltic rocks dredged from the first segment of the Southwest Indian Ridge near the Rodriguez Triple Junction have been completed in order to investigate water-rock interaction processes during mid-ocean ridge (MOR) hydrothermal alteration in the Indian Ocean. In the study area, we have successfully recovered a serial section of upper oceanic crust exposed along a steep rift valley wall which was uplifted and emplaced along a low angle normal fault. On the basis of microscopic observation, dredged samples are classified into three types: fresh lavas, low-temperature altered rocks, and high-temperature altered rocks. The fresh lavas have essentially the same chemical composition as typical N-MORB, although LILE and Nb are slightly enriched and depleted, respectively. Low temperature alteration brought about the enrichment of K2O, Rb, and U due to the presence of K-rich celadonite and U-adsorption onto Fe-oxyhydroxide and clay minerals. On the other hand, chloritization, albitization, and addition of base metals by high temperature hydrothermal alteration result in enrichments of MnO, MgO, Na2O, Cu, and Zn and depletions of CaO, K2O, Cr, Co, Ni, Rb, Sr, and Ba. In addition, U-enrichment is also observable in the high temperature altered rocks probably due to the decrease of uranite solubility in the reducing high-temperature hydrothermal solution. These petrological and geochemical features are comparable to those of the volcanic zone to transition zone rocks in the DSDP/ODP Hole 504B, indicating that our samples were recovered from the upper ~1000 m section of the oceanic crust. Only the alteration minerals related to off-axis alteration are absent in our samples dredged from near the spreading axis. The similarity of alteration between our samples from the Indian Ocean and the Hole 504B rocks from the Pacific Ocean suggests that MOR hydrothermal systems are probably similar across all world oceans.

Noble gas concentrations of oceanic crust and sediments from the Ninety East Ridge in the Indian Ocean

We have determined the concentrations and isotopic composition of noble gases in old oceanic crust and oceanic sediments and the isotopic composition of noble gases in emanations from subduction volcanoes. Comparison with the noble gas signature of the upper mantle and a simple model allow us to conclude that at least 98% of the noble gases and water in the subducted slab returns back into the atmosphere through subduction volcanism before they can be admixed into the earth's mantle. It seems that the upper mantle is inaccessible to atmospheric noble gases due to an efficient subduction barrier for volatiles.

Characteristics of light and dark alternations in Owen Ridge sediments (Appendix)

Clay mineral relative abundances in approximately 450 samples from cores recovered during ODP Leg 117 in the Arabian Sea have been used to examine the paleoclimatic, paleoenvironmental, and tectonic histories of the Indus Fan, Owen Ridge, Oman margin, and adjacent continental source regions. Geographic variations in the relative abundances of minerals and correlations with depositional processes support previous interpretations that smectite has been supplied from weathering of the Deccan Traps; illite and chlorite have been supplied either from the Himalayas via marine transport or from the Iran-Makran region by winds; and palygorskite has been supplied from the Arabian peninsula and Somalia by winds. Pleistocene sediments of the Indus Fan record two modes of deposition: turbidites supplied from the Indus drainage and dominated by illite and chlorite, and pelagic carbonates containing smectites and wind-transported palygorskite. Local and regional causes for shifts between these depositional processes cannot be demonstrated conclusively with the data available, but sea-level fluctuations probably exerted a significant control on the rate of turbidite influx. Lower Miocene sediments on the Owen Ridge are also turbidites supplied by the Indus drainage; in the middle Miocene, a shift to pelagic carbonates records the uplift of the Owen Ridge, and is accompanied by the increased relative importance of wind-transported palygorskite. Associations of palygorskite and biosiliceous components in middle to upper Miocene sediments are interpreted to record vigorous monsoonal circulation and accompanying upwelling-produced biological productivity. Mineralogic and geochemical data indicate that light/dark color alternations in upper Miocene sediments on the Owen Ridge record climatic fluctuations, but the climatic significance of similar alternations in Pliocene-Pleistocene sediments is unclear. Palygorskite is the dominant clay on the Oman margin, reflecting proximity to its source areas. On the Oman margin, clay mineral relative abundances are most variable at structurally complex sites, indicating that local depositional settings have been influenced by their tectonic histories since the Miocene.